Method for defining a sports or playing area by means of a thermochromatic spin transition material

ABSTRACT

A surface marking method using a thermochromatic spin transition material.

The present invention relates to a novel method for marking surfaces.

In many applications, it is necessary to mark surfaces reversibly. Thus, this is notably the case of sports grounds and more specifically multi-sport halls. Up to now, the surface of the ground is marked by the different delimitations of several grounds corresponding to distinct sports. However, the entanglement of different delimitations makes them difficult to read, both for sportsmen and for referees.

It is therefore desirable to make available a novel reversible method for marking surfaces, by means of which the delimitations of each ground may be made visible selectively and then made to disappear to the benefit of those of another ground.

Further, within the scope of marking surfaces, it would be quite interesting to be able to detect contact with these marked surfaces. Indeed this would allow detection of the impact of a ball or of any other projectile, or contact by a sportsman and this for assisting with the task of referees. Indeed, the problems related to referee decisions in the sporting community have lead to assisting refereeing with video, with which, in the case of a doubt of the referee on a disputed action (for example, passing over a line), it is possible to resort to slow motion of the played actions. The drawback of this device is the requirement of stopping the game and waiting for the decision taken by third parties. With detection of the impact or contact, directly on the marked line, it would therefore be possible to avoid resorting to this device and to referee in real time.

The present invention therefore proposes to solve these different problems by making available a novel method for marking surfaces.

Thermochromatic spin transition materials exhibit a change in magnetic and optical properties corresponding to an intra-molecular displacement of electrons. Thus, the spin transition phenomenon at a given temperature is accompanied by a change in color. Nevertheless, the applications of such materials for selective marking of surfaces, notably in the sporting community, have never been contemplated. Moreover, the feasibility of devices comprising these compounds as well as their use and their lifetime, notably under outdoor conditions, had not been suggested.

Thus, according to a first object, the present invention relates to a method for delimiting a sports or playing ground, said method comprising on said ground:

-   -   the application of a thermochromatic spin transition material         having a spin transition temperature above room temperature, on         the pre-marked delimitation lines or surfaces of said sports         ground or playing ground,     -   raising the temperature of said lines or surfaces to a         temperature above the spin transition temperature of said         material.

The present invention is based on the discovery that thermochromatic spin transition compounds, selected beforehand according to their spin transition temperature and having a significant, instantaneous and reversible change in color, with or without thermal hysteresis (memory effect), enable the making of a heat-sensitive paint with which the surfaces may be selectively delimited. This finds a quite original and unexpected application in the field of multi-sports grounds, for example.

The spin transition phenomenon has a corrosion-less effect which does not exhibit any fatigability. The detection principle is based on the fact that by applying heating, the spin transition material will switch on either side of its spin transition temperature from the low spin state to the high spin state. This transition induced by the temperature increase of the material is accompanied by a change in color of the latter.

Raising the temperature has the purpose of raising the temperature of said material to a temperature above said spin transition temperature. This may be achieved by any means known per se. Thus, mention may notably be made of having an electric current pass in a heating resistor positioned on the ground to be marked, prior to applying said spin transition material.

Mention may also be made of passing hot air over the marked ground, for example by blowing hot air.

The effect may either be self-reversible or not depending on the nature of the spin transition material used. By self-reversible is meant the capacity of the spin transition material of returning from its high spin state to its low spin state, instantaneously, only because its temperature returns to room temperature, upon stopping the heating (stopping the current in the heating resistor or stopping the passing of hot air).

Thus, if a self-reversible effect is desired, a spin transition material without any hysteresis is preferentially used. Thus, as long as the material is heated and maintained at a temperature above its transition temperature, the high spin color is maintained. On the other hand, as soon as the cooled material returns to a temperature below the spin transition temperature, the material returns to its initial low spin color. Thus, for marking the areas of a playing ground and/or sports ground, it is sufficient to maintain the delimitation lines at a temperature above the temperature for the spin transition of the material used. This embodiment notably applies when raising the temperature of the spin transition material is achieved by having a current pass into a heating resistor positioned on the surface to be marked, prior to applying the said material. In order to cause disappearance of the color, it is sufficient to decrease the temperature, for example by returning to room temperature, by stopping the current.

If, on the other hand, a self-reversible effect is not desired, a spin transition material with hysteresis has to be used. The hysteresis cycle comprised between T_(low spin) and T_(high spin) should be such that T_(low spin)<T_(room)<T_(high spin), so that the heated material retains its high spin color, even at room temperature. Thus, for marking the different areas of a sports ground and/or playing ground, it is sufficient to heat once the delimitation lines on which the material has been applied at a temperature above the spin transition temperature (or T_(high spin) in the case of a material with hysteresis). Once the transition has been effected and the high spin color has appeared, the material may return to room temperature, while retaining its high spin color. This embodiment advantageously applies in the case when raising the temperature is achieved by passing of hot air. A compound with hysteresis may however also be used with the passing of a current in the heating resistor so as to obtain an upper temperature T_(high spin), and then stopping the current, with the high spin color being maintained.

In order to cause this appearance of the high spin color of the material with hysteresis, it is then necessary to decrease the temperature to a temperature below T_(low spin). This may notably be achieved by passing cold air, notably by blowing cooled air.

The thermochromatic spin transition materials suitable for the invention may be selected from any thermochromatic spin transition material, having a spin transition temperature above room temperature, with or without thermal hysteresis. The selection of the materials is therefore made notably according to the transition temperature. Thus, as this is explained above, it is suitable to select a spin transition temperature above room temperature, but, for reasons of saving energy and of safety (risks of burns), this spin transition temperature will have to be selected as low as possible. Thus, the thermochromatic spin transition materials suitable for the invention have a spin transition temperature above room temperature, notably comprised between 20° C. and 85° C.

Thus, the spin transition material will be suitably selected according to the ambient temperature of the relevant sports ground/playing ground. Thus, for indoor sports grounds, where the temperature is regulated to be 18° C., a material for which the spin transition temperature is comprised between 20° C. and 85° C. may be used. For outdoor sports, such as tennis, where the temperature of the ground may be very high, the maximum temperature which the ground may attain should be determined in order to select a material for which the spin transition temperature is above this maximum temperature.

The materials suitable for the invention also have to be selected according to their high spin and low spin color so that the switching from one color to another is perfectly clear. Further, the color in the high spin state should be well visible to the users. Thus, the inventors have discovered that thermochromatic spin transition materials comprising iron and more preferentially the triazole or pyrazine ligand, optionally substituted, were suitable for the method according to the invention. Thus, mention may notably be made of compounds of the following formulae (I) or (II):

Fe(R-trz)₃R′₂  (I)

wherein

R, a substituent of the triazole ligand, represents a hydrogen atom or a group selected from amino or C₂-C₁₀ alkyl groups, and

R′, a counter-ion, is the NO₃ ⁻, BF₄ ⁻, Br⁻ or p-toluenesulfonate (p-tol) anion; and trz represents the triazole ligand

or

Fe(pz)M(CN)₄  (II)

wherein

pz represents the pyrazine ligand, and

M represents a metal selected from Pt, Pd, Ni.

Preferentially, this substituent of the triazole group is located in position 4 of the triazole group. Mention may thus be notably made of the following compounds:

Fe(4-NH₂-trz)₃(NO₃)₂, Fe(4-NH₂-trz)₃(BF₄)₂, Fe(4-NH₂-trz)₃Br₂, [Fe(4-n-butyl-trz)₃][p-tol]₂, [Fe(4-n-pentyl-trz)₃][p-tol]₂, [Fe(4-n-hexyl-trz)₃][p-tol]₂, [Fe(4-n-heptyl-trz)₃][p-tol]₂, [Fe(4-n-heptyl-trz)₃]Br₂, Fe(pz)Pt(CN)₄, Fe(pz)Pd(CN)₄, Fe(pz)Ni(CN)₄.

The aforementioned materials including a triazole ligand have a white color in the high spin state, whereas in the low spin state they are pink/violet. The aforementioned materials including a pyrazine ligand have a red color in the high spin state while in the low spin state they are yellow.

The compounds of formula (I) wherein R represents a 4-amino group are notably described in Journal of Structural Chemistry, 1995, 36, 1, 120-127.

The compounds of formula (I) wherein R represents a 4-alkyl group and R′ represents a p-toluenesulfonate anion are notably described in New J. Chem., 2001, 25, 144.

The compounds of formula (I) wherein R represents a 4-n-heptyl group and R′ represents a Br⁻ anion, is notably described in the article Synthetic Metals, 2004, 142, 243.

In the embodiment of the method according to the invention where raising the temperature is achieved by having an electric current pass into a heating resistor, it is preferable to apply a conducting material plate between said heating resistor and said spin transition material. The effect of this conducting material plate is to homogenize the temperature and therefore limit overheating phenomena which may be caused by the heating resistor. Thus, a metal plate is perfectly suitable for this purpose.

The method according to the invention may also comprise the application of a heat-insulating material layer on said surface to be marked, and this prior to optional application of said heating resistor. As an insulating material, mention may notably be made of polyurethane, as a layer for example with a thickness comprised between 0.1 and 5 mm. Polyurethane plates made by Allrin and marketed by Périchard Plastiques are quite suitable for the method according to the invention.

As a heating resistor, mention may be made of any conducting metal wire customarily used for this purpose. Generally, a resistance comprised between 1 and 100 Ω/m is suitable, preferentially about 25 Ω/m. The resistance may notably be controlled by a temperature controller.

The thereby formed electric circuit may also comprise any electric component, known per se, with which the performances of the heating device may be improved.

Applying the current into the resistor may be accomplished with the mains or by means of a generator. A current with an intensity comprised between 0.1 and 5 A, preferentially less than about 1 A, is generally suitable.

When raising the temperature is achieved by applying hot air on said lines or surfaces, this may notably be achieved by any means known per se, notably by means of a hot air blowing system based on the principle of a hair dryer, which is passed over the delimitation lines or surfaces.

Applying the thermochromatic spin transition material is preferentially carried out by means of a composition comprising said material, mixed in a polymer base and optionally a solvent. Thus, as a polymer, mention may notably be made of polyvinyl acetate, and as a solvent, acetonitrile or water.

According to an advantageous embodiment, the composition comprises between 10% and 90% of polymers and between 90% and 10% of the spin transition material (in moles). A particularly advantageous composition comprises 20% molar of spin transition material and 80% molar of polyvinyl acetate. The composition is made by mixing these ingredients in a solvent base such as acetonitrile.

Application of the composition comprising the spin transition material may be accomplished by applying a paint comprising said material or optionally by spin coating. This technique which is widely used, is for example described in EP 1 430 552. It consists in depositing a fluid on a support by centrifugation (or with a <<whirler>>), and then optionally evaporating the solvent. The spin transition material is deposited as a mixture with an inactive matrix, generally a polymer.

By <<spin transition temperature>> is meant the temperature at which the material switches from its low spin state to the high spin state. Thus, for a material without any hysteresis, said material has a single transition temperature, the transition from the high spin state to the low spin state occurring at the same temperature. On the other hand, for a material with hysteresis, said material has two transition temperatures: the lowest (T_(low spin)) allowing the switching from the high spin state to the low spin state upon cooling, and the highest (T_(high spin) called here <<the spin transition temperature>>) allowing switching from the low spin state to the high spin state upon heating.

Within the scope of the invention, the materials are selected from materials without any hysteresis for which the spin transition temperature is above room temperature or from materials with hysteresis for which one spin transition temperature is above room temperature.

By sports or playing areas are notably meant sports grounds or playing grounds or further any other surface for which delimitation by lines or surfaces has an importance in the practice of a sport or a game. Mention may thus be made of targets or further take-off boards used in jumping.

By delimitation lines or surfaces are meant lines or surfaces delimiting a sports or playing area or particular zones of the latter.

According to another object, the present invention relates to any sports or playing area which may be obtained by the method according to the invention.

It also relates to the method for making a delimitation line or surface of a sports or playing area comprising the application of a spin transition material as defined above on a heat-insulating material.

It also relates to any line or surface for delimiting a playing area which may be obtained by the method according to the invention.

According to another object, the present invention also relates to the device with which the method according to the invention may be achieved. Thus, said device comprises:

-   -   a thermally and electrically insulating material (2);     -   a heating resistor (1) positioned on said insulating material         (2);     -   a plate of conducting material (4) on said resistor (1); and     -   a thermochromatic spin transition material (3), with or without         thermal hysteresis, on said conducting material plate (4), said         spin transition material (3) having a spin transition         temperature above room temperature.

The figures between brackets refer to FIG. 1.

The invention will be better understood by means of FIG. 1 which is an exploded view of the device according to the present invention and wherein the resistor (1) is placed on the insulating material (2) and under a conducting material plate (4), itself supporting a layer of a composition comprising the spin transition material (3).

For applying the method according to the invention, the device is applied on lines or surfaces for delimiting sports or play surfaces, on which the lines or surfaces have been pre-marked by any means.

The present invention also relates to the use of the device according to the invention for marking surfaces. It also relates to the use of a thermochromatic spin transition spin material having a spin transition temperature above room temperature for delimiting sports or playing areas.

According to a particularly advantageous embodiment, the surfaces marked according to the invention may also detect contact or impact. Thus, the applied thermochromatic spin transition material has to have a transition temperature above room temperature on the one hand, and also above the temperature of the projectile or of the user in contact with said marked surface on the other hand. Thus, the marked surfaces may allow visual detection of the contact or impact with the marked surface. This is particularly advantageous for sports refereeing. The marked surfaces, when they are in contact with a projectile or a user, at a temperature below the temperature at which the marked surface is maintained, switch down to the low spin state and thereby change color. The detection principle is based on the fact that the impact of a projectile of the contact of a user, which has a temperature T1 (generally T1 is comprised between 0° and 40° C. taking into account extreme weather conditions and the heating-up of projectiles) will cool, upon the impact or contact, the thermosensitive marked surface containing the spin transition compound initially brought to a temperature T2 (T2>T1 et 20<T2<85° C., taking into account extreme weather conditions and risks of burns). The lowering of the temperature induced by the contact or the impact on the marked surface is accompanied by a change in color of the latter. The effect is irreversible at the same temperature when advantageously, the spin transition compound exhibits thermal hysteresis. This memory effect thus allows the referees to view a posteriori the impact or contact zone on the surface. Once detection is made, the marked surface may resume its initial color, by raising the temperature. This may be done at any moment and by simply controlling the temperature.

For achieving this particular embodiment, mention may notably be made of the complex [Fe(trz)₃](NO₃)₂. The latter has a sudden spin transition with thermal hysteresis which is accompanied by a change in color. The compound with a violet color at room temperature becomes white when it is heated beyond 79° C. The reverse process occurs when the material is cooled by contact or impact to 71° C. This compound therefore allows both marking of surfaces, the thermosensitive line will be heated to 80° C. (switching from the violet color to the white color) in order to view the delimitation of the ground; and viewing the impact or contact having the effect of lowering the temperature, notably by at most 2° C., which will cause the system to switch to the low spin state. Thus, the touched or impacted zone will change color and a zone of violet color, corresponding to the impact or contact zone will appear. Moreover, this change in color, well visible on the white line, is perfectly localized at the point of impact or contact. It is visible as long as the thermostated line is not again heated up beyond this transition temperature (79° C.). This process may be repeated at will depending on the state of the line of thermosensitive paint.

For this preferential embodiment, said contact is preferentially selected from the impact of a shot, a ball or projectile, or the contact of a user.

Said spin transition material has thermal hysteresis and is preferentially selected from spin transition materials having a spin transition temperature comprised between 50° C. and 85° C.

The thermally and optionally electrically insulating material applied on the area to be marked, prior to the optional application of the heating resistor is advantageously selected so that its heat transmission coefficient is smaller than that of the projectile or user in contact with it and the impact or the contact of which is to be detected. For this purpose, polyurethane may notably be mentioned.

Thus, according to another object, the present application therefore also relates to a method for detecting contact on a delimitation line or surface for a sports or playing area comprising:

-   -   delimitation of the sports or playing area according to the         invention;     -   detection of the changing color of the thereby marked line or         surface at the contact point.

The present invention also relates to the use of a thermochromatic spin transition material with hysteresis having a spin transition temperature comprised between 50° C. and 85° C. for detecting contact on a surface.

The following examples are also given as an illustration of the present invention.

EXAMPLE 1 Synthesis of the complex [Fe(trz)₃](NO₃)₂

This compound may be prepared according to Varnek et al., Journal of Structural Chemistry, 1995, 1, 36, 120-127. More specifically, the complex was prepared by mixing 0.005 mol of Fe(NO₃)₂ and 0.015 mol of 4-amino-1,2,4-triazole, solubilized in ethanol. The solution is dry evaporated and the white residue is washed with ethanol.

EXAMPLE 2 Depositing the Spin Transition Material on a Surface

The complex obtained in Example 1 is mixed with a polymer base such as polyvinyl acetate in amount of 40% molar of the complex. The mixing is carried out in acetonitrile with stirring. The deposition is then carried out on a polyurethane plate with a thickness of 5 mm. This deposition is achieved by spin coating, during which the solvent is evaporated.

EXAMPLE 3 Thermochromism Tests

The polyurethane layer covered with the complex is placed in an oven maintained at 72° C. Violet at room temperature, it switches to a white color in the oven.

Still in the oven, the plate is touched: the area of contact with the user becomes violet.

The operation is repeated by throwing a tennis ball onto the plate maintained in the oven. The impact area becomes violet instantaneously.

This violet spot persists at the impact point of the ball and at the contact point. By heating to a temperature above 79° C., the violet spot becomes white again.

EXAMPLE 4 Surface Marking Device

First of all a heating resistor of 25 Ω/m is attached on a polyurethane plate according to Example 2. A conducting metal plate is then applied, for example copper on the resistor. The composition is then applied by spin coating according to Example 2.

EXAMPLE 5 Thermochromism Test by Means of the Heating Device

A 0.4 A current is passed into the circuit consisting of the heating resistor. The layer of the composition, initially violet becomes white, when the temperature becomes greater than the low spin→high spin transition temperature. The same contact and impact tests are conducted as in Example 3, by maintaining the current in the electric circuit. The same phenomena occur. 

1-30. (canceled)
 31. A method for delimiting a sports or playing area, said method comprising on said area: the application of a thermochromatic spin transition material having a spin transition temperature above room temperature, on the lines or surfaces for delimiting said surface, raising the temperature of said lines or surfaces to a temperature above the spin transition temperature of said material.
 32. The method according to claim 31 such that said spin transition material is selected from spin transition materials having a spin transition temperature comprised between 20° C. and 85° C., with or without thermal hysteresis.
 33. The method according to claim 31 such that said material is selected from thermochromatic spin transition materials comprising iron.
 34. The method according to claim 31 such that said material is selected from thermochromatic spin transition materials comprising a ligand selected from the triazole (trz) or pyrazine (pz) ligands, optionally substituted.
 35. The method according to claim 31 such that said material is selected form compounds of formula: Fe(R-trz)₃R′₂ wherein: R, a substituent of the triazole ligand represents a hydrogen atom or a group selected from amino, C₂-C₁₀ alkyl groups, R′, a counter-ion, is the NO₃ ⁻, BF₄ ⁻ or p-toluenesulfonate (p-tol) anion.
 36. The method according to claim 31 such that said material is selected from the compounds of formula: Fe(pz)M(CN)₄  (II) wherein M represents a metal selected from Pt, Pd, Ni.
 37. The method according to claim 31 such that the spin transition material is selected from the following compounds: Fe(4-NH₂-trz)₃(NO₃)₂, Fe(4-NH₂-trz)₃(BFd₄)₂, Fe(4-NH₂-trz)₃Br₂, [Fe(4-n-butyl-trz)₃][p-tol]₂, [Fe(4-n-pentyl-trz)₃][p-tol]₂, [Fe(4-n-hexyl-trz)₃][p-tol]₂, [Fe(4-n-heptyl-trz)₃][p-tol]₂, [Fe(4-n-heptyl-trz)_(3]Br) ₂, Fe(pz)Pt(CN)₄, Fe(pz)Pd(CN)₄, Fe(pz)Ni(CN)₄.
 38. The method according to claim 31 such that the application of said spin transition material comprises the application of a composition comprising said material mixed in a polymer base, and optionally a solvent.
 39. The method according to claim 38 such that the polymer is polyvinyl acetate.
 40. The method according to claim 38 such that the solvent is acetonitrile or water.
 41. The method according to claim 31 such that the application of the spin transition material is accomplished by spin coating.
 42. The method according to claim 31 such that said rise in temperature is achieved by having an electric current pass into a heating resistor positioned on said delimitation lines or surfaces, prior to the application of said material.
 43. The method according to claim 42 such that said method further comprises the application of a conducting material plate between said heating resistor and said spin transition material.
 44. The method according to claim 31 such that the rise in temperature is achieved by having hot air pass over said lines or surfaces.
 45. The method according to claim 44 such that the spin transition material has thermal hysteresis.
 46. The method according to claim 31 such that said method further comprises the application on said line or surface of an insulating material layer, prior to the optional application of said heating resistor and prior to the application of said material.
 47. The method according to claim 46 such that said insulated material is polyurethane.
 48. A sports or playing area which may be obtained by the method according to claim
 31. 49. A method for making a line or surface for delimiting a sports or playing area comprising the application of a spin transition material as defined according to claim 31 on a heat-insulating material.
 50. A line or surface for delimiting a playing area which may be obtained by the method of claim
 49. 51. A method for detecting contact on a line or surface for delimiting a sports or playing area comprising: delimitation of the sports or playing area according to claim 31; detection of the change in color of the thereby marked line or surface at the contact point.
 52. The method according to claim 51 such that said contact is selected from the impact of a shot, ball or projectile or the contact of a user.
 53. The method according to claim 51 such that said spin transition material is selected from spin transition materials having a spin transition temperature comprised between 50° C. and 85° C.
 54. The method according to claim 51 such that said spin transition material has thermal hysteresis.
 55. The method according to claim 51 such that said spin transition material is the compound of formula: Fe(trz)₃(NO₃)₂.
 56. A device comprising: an insulating material (2); a heating resistor (1) positioned on said insulating material (2); a conducting material plate (4) on said resistor and a thermochromatic spin transition material (3) on said conducting material plate, said spin transition material having a spin transition temperature above room temperature.
 57. The device according to claim 56, wherein the device is configured to be applied on lines or surfaces for delimiting said lines or surfaces with said spin transition material.
 58. A method for marking surfaces, comprising marking said surfaces with the device of claim
 56. 59. A thermochromatic spin transition material having a spin transition temperature above room temperature, for delimiting a sports or playing area.
 60. The thermochromatic spin transition material according to claim 59, having a spin transition temperature comprised between 50° C. and 85° C. with hysteresis for detecting contact on a surface. 